Native Vlan Tagging

[vsurresh]

Hello experts,

I am a bit confused regarding the native VLAN behavior. I came across such a network set up .

R1-----SW03------SW02--------SW01------IP Phone-----PC

Note - There are some other customers also connected to SW01 and using different VLANs.

IP Phone is on VLAN 2, PC is on VLAN 10

SW01's Gi0/1 is connecting to IP phone

interface GigabitEthernet0/1

 switchport trunk encapsulation dot1q

 switchport trunk native vlan10

 switchport trunk allowed vlan 2,10

 switchport mode trunk

SW01's Gi0/2 is connecting to SW02

interface GigabitEthernet0/2

 description "To SW02"

 switchport trunk encapsulation dot1q

 switchport trunk allowed vlan 1-4,10,14-21

 switchport mode trunk

SW02's Gi0/1 is connecting to SW01

 

 interface GigabitEthernet0/1

 description "Connection to SW01"

 switchport trunk encapsulation dot1q

 switchport trunk allowed vlan 1-4,10,14-21

 switchport mode trunk

 switchport nonegotiate

SW02's Gi0/2 is connecting to SW03

interface GigabitEthernet0/2

 description " to SW03"

 switchport trunk encapsulation dot1q

 switchport trunk allowed vlan1-4,10,14-21

 switchport mode trunk

 switchport nonegotiate

SW03's Gi0/1 is connecting to SW02

interface GigabitEthernet0/27

 description "Connection to SW02"

 switchport trunk encapsulation dot1q

 switchport trunk allowed vlan1-4,10,14-21

 switchport mode trunk

 switchport nonegotiate

SW03's Gi0/2 is connecting to R1

 interface GigabitEthernet0/2

 description to R1

 switchport trunk encapsulation dot1q

 switchport trunk allowed vlan 1-4,10,14-21

 switchport mode trunk

 SW01#show inter trunk

Gi0/1       on           802.1q         trunking      10

Gi0/2      on           802.1q         trunking      1

SW02#show inter trunk

 Port        Mode         Encapsulation  Status        Native vlan

Gi0/1      on           802.1q         trunking      1

Gi0/2      on           802.1q         trunking      1

 SW03#show inter trunk

 Gi0/1     on           802.1q         trunking      1

Gi0/2    on           802.1q         trunking      1

Whats the point of creating a Native VLAN of 10 on SW01? Would all the traffic form different VLANs would be segregated when reaching SW3/R1?  

Please let me know if you need more configs?

Thanks in advance :)

[Martin Carr]

I didn't state his phones are using CDP, that was a general statement to the Voice VLAN command.

We cannot tell anything of his phone configuration from what has been posted.

I disagree that both are on the same VLAN. 

As I say, I suspect that the data VLAN is 10 and the Voice VLAN is 2.

Martin

[burleyman]

I could be wrong because I have never seen this setup this way nor would I but I may have to just lab this up and check it out. Learning is good.

Mike

[burleyman]

So I can understand this.

If I have 2 DHCP pools one for phones and one for PCs.

PCs - 10.1.1.0 /24 - VLAN 2

Phones - 10.1.2.0 /24 - VLAN 10

With the port configured like this....

interface GigabitEthernet0/1

 switchport trunk encapsulation dot1q

 switchport trunk native vlan10

 switchport trunk allowed vlan 2,10

 switchport mode trunk

Then I connect a new phone it will get an IP address in VLAN 10.

Now I connect a PC into the phone and since it know no difference between a phone and a PC it to will get an IP address in VLAN 10, correct? or what am I missing?

Mike

[Joseph W. Doherty]

"Then I connect a new phone it will get an IP address in VLAN 10."

Maybe, maybe not. It could pull an IP from VLAN 2. It depends on the phone. For example, it might be hard coded to use VLAN tags for VLAN 2. (I've also worked with brand "X" phone that would come up untagged, receive a DHCP option informing them to switch to a tagged VLAN.)

"Now I connect a PC into the phone and since it know no difference between a phone and a PC it to will get an IP address in VLAN 10, correct? or what am I missing?"

Usually VoIP phones will connect a downstream PC to the untagged VLAN, regardless of whether the phone, itself, is using untagged or tagged frames. I.e. I would expect the PC to be on VLAN 2.

[burleyman]

Thanks for the info. I have never needed to connect non-cisco phones or have to deal with them. In searching on this I did come across the DHCP option to set the VLAN to the phone here...

https://supportforums.cisco.com/t5/lan-switching-and-routing/voice-vlan-for-non-cisco-phones/td-p/1889572

Good information, learn something new everyday, great stuff.

Mike

[vsurresh]

Hi guys,

Thanks for your input.

We currently use Mitel phones which supports LLDP. Whoever configured the device they did it in such a way as voip traffic get tagged with vlan 2. And configured data traffic as native (which will get tagged with vlan 10)

It just works fine, but I realised the best practice is to use access vlan and voice vlan.

[Martin Carr]

Yes, as I thought.

Martin

[vsurresh]

Hi Joseph,

'phone that would come up untagged, receive a DHCP option informing them to switch to a tagged VLAN.'

You are right :)